WO2009112259A1

WO2009112259A1 - Edging system for panels having a cellular structure, particularly for honeycomb panels

Info

Publication number: WO2009112259A1
Application number: PCT/EP2009/001777
Authority: WO
Inventors: John Blancaneaux
Original assignee: Zephyros Inc
Priority date: 2008-03-12
Filing date: 2009-03-12
Publication date: 2009-09-17
Also published as: GB0804554D0

Abstract

Edging strips for honeycomb structures (3) are foamable and cart be softened and foamed in contact with the edge of the honeycomb structure to bond to the honeycomb. A convenient in situ heating system is also provided comprising a, U or C shaped heater (4) which can be placed around the edge of the honeycomb structure carrying the edging material and activated to bond the edging material (2) to the honeycomb structure.

Description

EDGING SYSTEM

The present invention relates to improvements in or relating to the edging of cellular structures and in particular to providing edge material to foamed or honeycomb structures. The invention is further concerned with apparatus for the provision of edging to cellular structures.

Cellular structures have many applications where it is desired to provide strength at light weight and/or to provide thermal or acoustic insulation. Examples of the use of honeycomb structures are in aircraft wings and the like. It is however necessary to close the edges of the honeycomb or cellular structure to provide additional strength and to protect it from damage. Edging is also required to prevent the ingress of undesirable contaminants and/or moisture into the structure which could cause breakdown of the structure and/or add to its weight. Edging may also be required to improve the appearance of honeycomb materials to hide the honeycomb structure from view.

Honeycomb structures often take the form of panel sandwich structures comprising the honeycomb provided with two facing panels and the edging material is provided to bridge the ends of the facing material and to cover the end of the honeycomb structure. Honeycomb structures are typically made from a variety of materials such as metals such as aluminium, plastics, cellulosics, paper etc.

Currently edging is provided to honeycomb structures by the application of a two component adhesive product and the application of an edging profile generally of plastic or aluminium. This is however a cumbersome and time consuming process; typically the application and curing of the material can take several hours. In many instances large ovens are required to bake the edging material. The present invention provides a simplified process for the production of edging material to cellular or honeycomb structures.

The present invention therefore provides a process for the provision of edging profile(s) to honeycomb structures comprising providing a heat activatable foamable edging profile adjacent to the edge of the honeycomb structure and heating the material to cause it to foam and to bond to the honeycomb structure. In a preferred embodiment the heating is provided by a heater shaped so that it can encompass the edge of the honeycomb structure provided with the edging profile,

The preferred method for heating the profile material will depend upon the nature of the material forming the honeycomb structure and the nature of the edging material.

Depending upon these factors the heating may be provided by induction heating, infra red heating, high frequency heating or conduction heating. The edging material may be applied by hand around the honeycomb structure or it may be applied mechanically. In a particular embodiment the edging material is a strip which may contain a conducting material which can be heated by induction so that the strip is softened and foamed by the heat generated by the conducting material and bonds to the edge of the honeycomb structure.

In a further embodiment an edge profile is adhered to the edge of the honeycomb structure by means of an intermediary layer. In this instance it is the intermediary layer that is of the heat foamable material which is chosen so that it can soften and cure to adhere to both the edge profile and the honeycomb structure. In this instance the choice of the edge profile material will depend upon the properties and appearance required for the edge of the structure. Examples of suitable materials from which the edge profile may be made include metal profiles such as aluminium or plastic profiles which may be of polyolefines such as polyethylene and polypropylene or polyamides which may or may not contain fillers. The use of a foamable material has the benefit that when the material foams it will expand to within the cells of the honeycomb structure thus increasing the area of contact between the edging material and the honeycomb so increasing the strength of the bond between the edging material and the honeycomb structure resulting in an overall strength increase.

Honeycomb structures may comprise a variety of core options and a variety of facing sheet options. The core may be of metal and examples of metals that may be used include aluminium, titanium, stainless steel and nickel-based super alloys. The core may also be of thermoplastic materials such as polypropylene or polycarbonate. Honeycombs with paper fibreglass, or cellulose cores are also known. The facing sheet options may also be metal such as steel, coated steel, aluminium, plastics such as polyvinyl chloride, polyolefines, polyamides which may or may not be reinforced with fibres such as glass fibre or carbon fibre. The techniques of the present invention are applicable to all honeycomb structures although the method of heating should be selected according to the materials from which the honeycomb core, and facings and the edging strips are made.

A smooth external surface may be provided by the use of a laminar edging material in which one layer is the foamable activatable material which is adjacent to the honeycomb structure. Alternatively pressure can be applied to the external surface of the activatable material to minimise the foaming of the surface layer.

The edging layer is typically substantially non-tacky to the touch at ambient temperature. As used herein, the term activatable is used to refer to adhesive materials that melt, flow, wet, cure (e.g., thermoset and/or harden), expand (e.g., foam) or any combination thereof due to external stimulus (e.g., heat, radiation, moisture).

The edging layer is typically comprised of at least one, but preferably any combination of two or more of the following: i. epoxy resin, a substantial portion of which is preferably a solid epoxy resin, a multi-functional resin or both; ii. elastomer containing adduct, a substantial portion of which is also preferably a solid and is preferably an epoxy/elastomer adduct; iii. an elastomer, a substantial portion of which is also preferably a solid; iv. impact modifier; v. thermoplastic resin; vi. curing agent; and/or vii. filler viii. blowing agent.

Epoxy resin is used herein to mean any of the conventional dimeric, oligomeric or polymeric epoxy materials containing at least one epoxy functional group. The polymer-based materials may be epoxy containing materials having one or more oxirane rings polymerizable by a ring opening reaction. In preferred embodiments, the edging layer includes a substantial amount of epoxy resin that is up to about 90% by weight of the handling layer. More preferably, the edging layer includes between about 30% and 80% by weight epoxy resin and still more preferably between about 50% and 70% by weight epoxy resin. The epoxy may be aliphatic, cycloaliphatic, aromatic or the like. The epoxy resin may be supplied as one or more solid resins (e.g., epoxy resin that is solid at 23⁰C and can be supplied as pellets, chunks, pieces or the like), one or more liquid (e.g., epoxy resin that is liquid at 23⁰C) or a combination of solid and liquid resins. The epoxy may include an ethylene copolymer or terpolymer that may possess an alpha- olefin. As a copolymer or terpolymer, the polymer is composed of two or three different monomers, i.e., small molecules with high chemical reactivity that are capable of linking up with similar molecules. One exemplary epoxy resin may be a phenolic resin, which may be a novalac type or other type resin. Other preferred epoxy containing materials may include a bisphenol-A epichlorohydrin ether polymer, or a bisphenol-A epoxy resin which may or may not be modified with, for example, a polymeric additive.

In preferred embodiments, one or more of the epoxy resins employed in the activatable material are multifunctional and/or have relatively high functionalities

(e.g., epoxy functionalities). When such relatively high functionality resins are employed, it is typically desirable for at least 2%, more typically at least 5% and even possibly at least 10 % of the epoxy resin to have a functionality that is greater than about 2 (e.g., about 2.6 or greater), more typically greater than about 3 (e.g., about 3.6 or greater) and still more typically greater than about 4.5 (e.g., about 5.1 or greater).

It is also generally preferable for a substantial portion of the epoxy resin to be comprised of one or more solid epoxy resins. Such one or more solid epoxy resins typically comprise at least about 50%, although possibly less, more typically at least 75%, even more typically at least 80% and still more typically at lest 93% by weight of the (or any) epoxy resin present in the handling layer. It is also contemplated that the (or any) epoxy resin of the handling layer is substantially entirely, entirely or consists essentially of solid resin such that the handling layer can be substantially or entirely without any liquid epoxy resin. Examples of suitable epoxy resins, without limitation, are sold under the trade designations DER^® 661 , 662, 664 or 331 and are commercially from Dow Chemical Company, Midland, Ml and under the trade designation ARALDITE GT 7071 , GT 7072, GT 7074 or 1280 ECN commercially available from Huntsman. Elastomer-containing Adduct

In a highly preferred embodiment, an elastomer-containing adduct is employed in the edging layer of the present invention, and preferably in a relatively high concentration (e.g., on the order of the epoxy resin). The epoxy/elastomer hybrid or reaction product (e.g., adduct) may be included in an amount of up to about 80% by weight of the adhesive material. More preferably, the elastomer-containing adduct is approximately or more exactly 7 to 70%, more preferably 20 to 60%, and even more preferably is about 20% to 35% by weight of the adhesive material. Of course, the elastomer-containing adduct may be a combination of two or more particular adducts and the adducts may be solid adducts or liquid adducts at a temperature of 23⁰C or may also be combinations thereof.

The adduct itself includes about 1 :5 to 5:1 parts of epoxy to elastomer, and more preferably about 1 :3 to 3:1 parts or epoxy to elastomer. More typically, the adduct includes at least about 5%, more typically at least about 12% and even more typically at least about 18% elastomer and also typically includes not greater than about 50%, even more typically no greater than about 40% and still more typically no greater than about 35% elastomer, although higher or lower percentages are possible. The elastomer compound may be any suitable art disclosed elastomer such as a thermosetting elastomer. Exemplary elastomers include, without limitation natural rubber, styrene-butadiene rubber, polyisoprene, polyisobutylene, polybutadiene, isoprene-butadiene copolymer, neoprene, nitrile rubber (e.g., a butyl nitrile, such as carboxy-terminated butyl nitrile), butyl rubber, polysulfide elastomer, acrylic elastomer, acrylonitrile elastomers, silicone rubber, polysiloxanes, polyester rubber, diisocyanate-linked condensation elastomer, EPDM (ethylene-propylene diene rubbers), chlorosulphonated polyethylene, fluorinated hydrocarbons and the like. In one embodiment, recycled tire rubber is employed. Examples of additional or alternative epoxy/elastomer or other adducts suitable for use in the present invention are disclosed in United States Patent Publication 2004/0204551.

The elastomer-containing adduct, when added to the edging layer preferably is added to modify structural properties of the adhesive material such as strength, toughness, stiffness, flexural modulus, or the like. Additionally, the elastomer- containing adduct may be selected to render the adhesive material more compatible with coatings such as water-borne paint or primer system or other conventional coatings.

According to one preferred embodiment, the edging layer includes a substantial portion of one or more solid adducts (i.e., solid at a temperature of about 23 ⁰C) for assisting in improving properties such as impact strength, peel strength, combinations thereof or others. Thus, in one embodiment, it is contemplated that for all adducts in the edging layer, the one or more solid adducts typically comprise at least about 50%, although possibly less, more typically at least 75%, even more typically at least 80% and still more typically at least 93% by weight of the or any adducts present in the handling layer. It is also contemplated that the, or any adduct of the edging layer is substantially entirely, entirely or consists essentially of adduct such that the edging layer can be substantially or entirely without any liquid adduct. Examples of suitable epoxy/elastomer adduct, without limitation, are sold under the trade designation HYPOX RK8-4, commercially available from CVC Chemical.

Elastomer

Generally, the edging layer can include one or more of a variety of elastomeric materials, which may be independently admixed into the adhesive material or may be added as part of a admixture of materials. Exemplary suitable elastomers include, without limitation, natural rubber, styrene-butadiene rubber, polyisoprene, polyisobutylene, polybutadiene, isoprene-butadiene copolymer, neoprene, butyl rubber, polysulfide elastomer, acrylic elastomer, acrylonitrile elastomers (e.g., butadiene/ acrylonitrile rubber), silicone rubber, polysiloxanes, polyester rubber, polyurethane rubber, diisocyanate-linked condensation elastomer, EPDM (ethylene- propylene diene rubbers), chlorosulphonated polyethylene, fluorinated hydrocarbons and the like

According to one preferred embodiment, the elastomer is partially or substantially entirely (e.g., at least 80%, 90%, 95% or more) or entirely composed of a nitrile rubber (e.g., a butadiene/acrylonitrile rubber). If such a nitrile rubber is employed, the rubber preferably includes between about 10% or less and about 50% or more by weight nitrile, more preferably between about 20% and about 40% by weight nitrile and even more preferably between about 25% and about 35% by weight nitrile. Advantageously, the elastomer can provide desired properties to the edging layer, such as toughness, flexibility or the like. When used, elastomer is typically at least about 1%, although possibly less, more typically at least about 5% and still more typically at least about 9% and possibly even at least about 12% by weight of the handling film. Moreover, when used, elastomer is also typically less than about 40%, although possibly more, more typically less than about 25% and even more typically less than about 18% by weight of the edging layer. Examples of desirable elastomers are sold under the tradenames NIPOL DN 3335, commercially available from Zeon Chemicals.

Blowing Agent

One or more blowing agents are included in the edging layer. The blowing agents may be chemical and produce inert gasses that form, as desired, an open and/or closed cellular structure within the layer or may be physical and either may be activated upon exposure to a condition such as heat, radiation, moisture, chemical reaction, combinations thereof or the like. In this manner, it may be possible to lower the density of articles fabricated from the layer.

The blowing agent may include one or more nitrogen containing groups such as amides, amines and the like. Examples of suitable blowing agents include azodicarbonamide, dinitrosopentamethylenetetramine, 4,4,-oxy-bis-

(benzenesulphonylhydrazide), trihydrazinotriazine and N, N-dimethyl-N.N,- dinitrosoterephthalamide. Other potential blowing agents include solvent encapsulated in thermoplastic shells.

An accelerator for the blowing agents may also be provided in the edging layer. Various accelerators may be used to increase the rate at which the blowing agents form inert gasses. One preferred blowing agent accelerator is a metal salt, or is an oxide, e.g. a metal oxide, such as zinc oxide. Other preferred accelerators include modified and unmodified thiazoles, hydrazides, imidazoles, ureas, combinations thereof or the like. Amounts of blowing agents and blowing agent accelerators can vary widely within the edging layer depending upon the type of cellular structure desired, the desired amount of expansion (e.g., foaming), the desired rate of expansion, desired cure conditions and the like. Exemplary ranges for the amounts of blowing agents and blowing agent accelerators in the edging layer range from about 0.001% by weight to about 5% by weight and are preferably in the adhesive material in fractions of weight percentages when used.

In one embodiment, the present invention contemplates the omission of a blowing agent. Thus, it is possible that the handling layer will not be a foamable material. Preferably, when used, the blowing agent of the present invention is thermally activated. However, other agents may be employed for realizing activation by other means, such as moisture, radiation, or otherwise.

Curing Agent

One or more curing agents and/or curing agent accelerators may be added to the edging layer. Amounts of curing agents and curing agent accelerators can vary within the edging material depending upon the desired structural properties of the expanded adhesive material, the desired cure conditions (e.g., manufacturing conditions) and the like. Exemplary ranges for the curing agents or curing agent accelerators present in the edging layer range from about 0.01% by weight to about 7% by weight.

Preferably, the curing agents assist the edging layer in curing by crosslinking of the epoxy containing adducts, epoxy resins (e.g., by reacting in stoichiometrically excess amounts of curing agent with the epoxide groups on the resins), other polymers or a combination thereof. It is also preferable for the curing agents to assist in thermosetting the edging layer. Useful classes of curing agents are materials selected from aliphatic or aromatic amines or their respective adducts, blocked amines, amidoamines, polyamides, cycloaliphatic amines, (e.g., anhydrides, polycarboxylic polyesters, isocyanates, phenol-based resins (such as phenol or cresol novolak resins, copolymers such as those of phenol terpene, polyvinyl phenol, or bisphenol-A formaldehyde copolymers, bishydroxyphenyl alkanes or the like), or mixtures thereof. Particular preferred curing agents include modified and unmodified polyamines or polyamides such as cyanoguanidine, hydrazides, sulphones (e.g., diamino diphenyl sulphone (DDS)), dicyandiamides and the like. An accelerator for the curing agents (e.g., a modified or unmodified urea such as methylene diphenyl bis urea, an imidazole or a combination thereof) may also be provided for preparing the activatable material.

Filler

The edging layer may also include one or more fillers, including but not limited to particulated materials (e.g., powder), beads, microspheres, or the like. Preferably the filler includes a relatively low-density material that is generally non-reactive with the other components present in the edging layer.

Examples of fillers include silica, diatomaceous earth, glass, clay, talc, pigments, colorants, glass beads or bubbles, glass, carbon ceramic fibers, antioxidants, and the like. Such fillers, particularly clays, can assist the activatable material in leveling itself during flow of the material. The clays that may be used as fillers may include clays from the kaolinite, illite, chloritem, smecitite or sepiolite groups, which may be calcined. Examples of suitable fillers include, without limitation, talc, vermiculite, wollastonite, pyrophyllite, sauconite, saponite, nontronite, montmorillonite or mixtures thereof. The clays may also include minor amounts of other ingredients such as carbonates, feldspars, micas and quartz. Titanium dioxide might also be employed.

One or more mineral or stone type fillers such as calcium carbonate, sodium carbonate or the like may be used as fillers. In another preferred embodiment, silicate minerals such as mica may be used as fillers.

When employed, the fillers in the edging layer can range from 2% to 40% by weight of the handling layer material. According to some embodiments, the edging layer may include from about 0.1 % to about 30 % by weight, and more preferably about 2% to about 20% or about 5 to about 10% by weight clays or other fillers. Powdered (e.g. about 0.01 to about 50, and more preferably about 1 to 25 micron mean particle diameter) mineral type filler or other fillers can comprise between about 1% and 70% by weight, more preferably about 3% to about 20%, and still more preferably approximately 6% by weight of the adhesive material. It is also contemplated that the activatable material may include one or more conductive materials as filler, which can assist in weld-through of the material. Examples of such materials includes graphite, carbon-black, iron phosphide, metal particulate (e.g., pellets, shavings or the like), combinations thereof or the like. When used, such conductive material typically comprises at least about 1%, more typically at least about 3% and even more typically at least about 7% by weight of the handling layer and also typically comprise less than about 30%, more typically less that about 15% and even more typically less than about 11 % by weight of the handling layer, although higher or lower amounts may be used. One exemplary desirable conductive filler is sold under the tradename FERROPHOS 2131 , commercially available from OxyChem Corporation. Other desirable conductive fillers are synthetic or natural graphites and/or carbon fibers sold under the tradename ASBURY and commercially available from the Asbury Corporation. In such an embodiment, the conductive filler may be substantially the only filler or the only filler of the edging layer, but unless otherwise stated, others can be included.

Formation

Formation of the edging material or layer may be accomplished according to a variety of methodologies. Generally, ingredients of the handling layer are typically mixed in a batch type process to form a substantially homogeneous mixture. For example, the ingredients may be dispensed to a mixer (e.g., a high shear mixer) and mixed until the material of the layer is formed in a substantially homogeneous state. Preferably, the mixing takes place at a temperature between about 50⁰C or lower and 250⁰C or higher, more preferably between about 70⁰C and about 200⁰C and even more preferably between about 80⁰C and about 160⁰C and even possibly between about 80°C and about 160°C. Thereafter, the material can be allowed to cool and typically solidify although it may cool and remain as a semi-solid or a liquid, unless otherwise stated.

In one embodiment, the edging layer is formed using a continuous mixing process such as by mixing the in an extruder or feeding the mixed ingredients as a solid, semi-solid or liquid to the extruder. In such an embodiment, the components or the material can be fed into an extruder at various different locations along the length of the extruder. Then, one or more screws of the extruder typically rotate and intermix and/or melt the ingredients such that the layer can be emitted as a layer from the extruder.

In one preferred embodiment, the material of the handling layer is provided (e.g., extruded) as a layer and then stretched to thin the layer and achieve a desired thickness of the handling layer. One exemplary technique for stretching the layer include extrusion of the handling layer onto a conveyor belt with the conveyor belt traveling at a rate that is faster than the rate at which the handling layer (i.e., the extrudate) leave the extruder. It is also possible, however, to use a die (e.g., an extrusion die) that emits a layer of a desired thickness to be the handling layer without subsequent stretching.

Generally, the activatable material may expand (e.g., foam) to at least about 101%, at least about 300%, at least about 500%, at least about 800%, at least about 1100%, at least about 1500 %, at least about 2000 %, at least about 2500% or at least about 3000% its original or unexpanded volume. Typically, an adhesive structural material of the present invention might expand, due to foaming, to a volume that is about 101 % to about 450% of the volume of the material prior to expansion. A sealing adhesive material might expand to a volume that is about 500% to about 4000% of the volume of the material prior to expansion (e.g., foaming). Of course higher or lower expansion levels are within the scope of the present invention unless otherwise specifically stated.

Other additives (e.g., polymers, agents or performance modifiers) may also be included in the activatable material as desired, including but not limited to a UV resistant agent, a flame retardant, an impact modifier, a heat stabilizer, a UV photoinitiator, a colorant, a processing aid, a lubricant, a reinforcement (e.g., chopped or continuous glass, ceramic, aramid (e.g., aramid fiber and/or pulp), or carbon fiber or the like).

The activatable material can also include core/shell impact modifier. Examples of core/shell impact modifier include, without limitation, core-shell graft copolymers where harder and/or higher glass transition temperature monomers or polymers, such as styrene, acrylonitrile or methyl methacrylate, are grafted onto cores made from polymers of soft or elastomeric containing compounds such as butadiene or butyl acrylate. United States Patent No. 3,985,703 describes useful core-shell polymers, the cores of which are made from butyl acrylate but can be based on ethyl isobutyl, 2-ethylhexel or other alkyl acrylates or mixtures thereof. The core polymer, may also include other copolymerizable containing compounds, such as styrene, vinyl acetate, methyl methacrylate, butadiene, isoprene, or the like. The core polymer material may also include a cross linking monomer having two or more nonconjugated double bonds of approximately equal reactivity such as ethylene glycol diacrylate, butylene glycol dimethacrylate, and the like. The core polymer material may also include a graft linking monomer having two or more nonconjugated double bonds of unequal reactivity such as, for example, diallyl maleate and allyl methacrylate.

The activatable material can also include additional polymeric materials which can include a variety of different polymers, such as thermoplastics, elastomers, plastomers combinations thereof or the like. For example, and without limitation, polymers that might be appropriately incorporated into the adhesive material or handling layer include, without limitation, halogenated polymers, polycarbonates, polyketones, urethanes, phenoxy resin (e.g., thermoplastic polyethers), polyesters, silanes, sulfones, allyls, olefins, styrenes, acrylates, methacrylates, epoxies, silicones, phenolics, rubbers, polyphenylene oxides, terphthalates, acetates (e.g., EVA), acrylates, methacrylates (e.g., ethylene methyl acrylate polymer) or mixtures thereof. Other potential polymeric materials may be or may include, without limitation, polyolefin (e.g., polyethylene, polypropylene) polystyrene, polyacrylate, poly(ethylene oxide), poly(ethyleneimine), polyester, polyurethane, polysiloxane, polyether, polyphosphazine, polyamide, polyimide, polyisobutylene, polyacrylonitrile, polyvinyl chloride), poly(methyl methacrylate), polyvinyl acetate), poly(vinylidene chloride), polytetrafluoroethylene, polyisoprene, polyacrylamide, polyacrylic acid, polymethacrylate. One preferred thermoplastic polymer is a copolymer of polyvinyl chloride and vinyl acetate.

Preferred thermoplastic polymers for the edging layer, the adhesive material or both such as polyamide, polyvinyl chloride, polyethylene or polypropylene and/or copolymers including such thermoplastic polymers will typically exhibit one or both of the following properties: glass transition temperature (T₉) between about 5O⁰C and about 15O⁰C and more typically between about 7O⁰C and about 12O⁰C; and a solubility parameter of between about 15 and about 32 J^1/2/cm^3/2 and more typically between about 18 and 26 J^1/2/cm^3/2. Such solubility parameter can be an indication of the miscibility of the thermoplastic polymer in an epoxy resin (e.g., a solid epoxy resin).

Honeycomb structures are used in a variety of applications where strength combined with light weight is desired. Examples of uses are in the aerospace and aircraft industries. Other industries include marine, automotive, rail, military, electrical and the construction industries.

The invention further provides an improved system and apparatus for the provision of the edging material. The system comprises a heater adapted to fit around the edge of the honeycomb structure with the edging material in position to provide direct heat to soften the edging material and cause it to foam and bond to the honeycomb structure. The heater may comprise a U or C shaped element which fits around the edge of the honeycomb structure. The heater may be an infra red heater, a radio frequency wave heater, an induction heater or a conduction heater.

The present invention is illustrated by the attached figures in which Figure 1 shows an adaptable frame (1) including an induction curing profile (4). The frame can be adapted around the honeycomb panel (3) with edge closeout material (2) positioned at the edge of the honeycomb. The edging material may be applied by an operator by hand all around the panel. The activation of the edging material is realized by heating temperature. The heating may be obtained by any suitable process such as induction, infrared, high frequency or conduction. Finishing of the edge closeout is realized by non adhesive surface included in the curing profile.

Figure 2 shows an adaptable frame (5) including induction curing profile. The frame can be adapted around the panel with the unfoamed edge closeout material provided at the edge of the honeycomb structure. This option uses non-foamable exterior profile such as a plastic or aluminum profile (6) for providing the surface finish. A very thin metallic film (7) is included between two edge closeout material sheets (8) and (9). The curing profile is used to elevate temperature of the metallic film by induction. This temperature between the two edge closeout sheets will activate the edge closeout material to expand the material to fill the cavity, glue the external profile, and reinforce locally the panel edge. Figure 3 shows an option employing a static curing system, like induction, infrared, convection, high frequency. The panel is finished with plastic or aluminum profile. The material is between the honeycomb cells and the profile. The honeycomb panel provided with the edge strips moves on a 2D plane at a pre-determined speed, to cure the material inside the panel.

The techniques of the present invention therefore provide a rapid process that provides edging to the honeycomb structure and also increases the strength of the structure. The edging can be provided in situ in less than 1 hour as opposed to existing techniques which can require 24 hours at room temperature of up to 8 hours at 60⁰C to 70⁰C. The techniques of the present invention do not require large ovens and the associated high energy and can conveniently be implemented at any desired location.

Claims

1. A process for the provision of edging profile(s) to honeycomb structures comprising providing a heat activatable foamable edging profile adjacent to the edge of the honeycomb structure and heating the material to cause it to foam and to bond to the honeycomb structure.

2. A process according to Claim 1 in which the heating is provided by a heater shaped so that it can encompass the edge of the honeycomb structure provided with the edging profile.

3. A process according to Claim 1 or Claim 2 in which the heating is provided by induction heating, infra red heating, high frequency heating or conduction heating.

4. A process according to any of the preceding claims in which the edging material is applied by hand around the honeycomb structure.

5. A process according to any of Claims 1 to 3 in which the edging material is applied around the honeycomb structure mechanically.

6. A process according to any of the preceding claims in which the edging material is a strip containing a conducting material which can be heated by induction so that the strip is softened and foamed by the heat generated by the conducting material and bonds to the edge of the honeycomb structure.

7. A process according to any of the preceding claims in which the edge profile is adhered to the edge of the honeycomb structure by means of an intermediary layer that is of the heat foamable material.

8. A process according to any of the preceding claims in which the edge profile is a metal profile such as aluminium.

9. A process according to any of Claims 1 to 7 in which the edge profile is of a polyolefine such as polyethylene and polypropylene or a polyamide which may or may not contain fillers.

10. A process according to any of the preceding claims in which the core of the honeycomb is selected from metal selected from aluminium, titanium, stainless steel and nickel-based super alloys; thermoplastic materials such as polypropylene or polycarbonate, paper, fibreglass and cellulose.

11. A process according to any of the preceding claims in which the facing sheet of the honeycomb is selected from metal such as steel, coated steel, aluminium and plastics such as polyvinyl chloride, polyolefines, polyamides which may or may not be reinforced with fibres such as glass fibre or carbon fibre.

12. A process according to any of the preceding claims in which a smooth external surface is provided by the use of a laminar edging material in which one layer is the foamable activatable material which is adjacent to the honeycomb structure.

13. A process according to any of the preceding claims in which a smooth external surface is provided by applying pressure to the external surface of the activatable material to minimise the foaming of the surface layer.

14. A process according to any of the preceding claims in which the edging layer is substantially non-tacky at ambient temperature.

15. A process according to any of the preceding claims in which the edging layer is of an epoxy based material.

16. A process according to Claim 15 in which the edging layer is comprised of at least one, but preferably any combination of two or more of the following:

i. epoxy resin, a substantial portion of which is preferably a solid epoxy resin, a multi-functional resin or both; ii. elastomer containing adduct, a substantial portion of which is also preferably a solid and is preferably an epoxy/elastomer adduct; iii. an elastomer, a substantial portion of which is also preferably a solid; impact modifier; iv. thermoplastic resin; v. curing agent; and/or vi. filler.

17. A system for the provision of the edging material comprising a heater adapted to fit around the edge of the honeycomb structure with the edging material in position to provide direct heat to soften the edging material and cause it to foam and bond to the honeycomb structure.

18. A system according to Claim 18 in which the heater comprises a U or C shaped element which fits around the edge of the honeycomb structure.

19. A system according to Claim 17 or Claim 18 in which the heater is an infra red heater, a radio frequency wave heater, an induction heater or a conduction heater.

20. An edged honeycomb structure wherein the edging is provided by a foamed material.

21. An edged honeycomb structure according to Claim 20 wherein the foamed material is an epoxy based material.

22. An edged honeycomb structure according to Claim 20 or Claim 21 wherein the honeycomb structure comprises a honeycomb core and two facing panels.